1. Field of the Invention
The present invention relates generally to polishing suitable for mass production of magnetic heads uniform in quality, and more particularly to a method and apparatus for polishing and a lapping jig.
2. Description of the Related Art
In a manufacturing process for a magnetic head, for example, a magnetic head thin film is formed on a substrate and next subjected to lapping (or polishing), thereby making constant the heights of a magnetic resistance layer and a gap in the magnetic head thin film. The heights of the magnetic resistance layer and the gap are required to have an accuracy on the order of submicrons. Accordingly, a lapping machine for lapping the magnetic head thin film is also required to have a high working accuracy.
FIGS. 1A and 1B illustrate a composite magnetic head in the related art. As shown in FIG. 1A, the composite magnetic head has a magnetic resistance element 2 formed on a substrate 1, and a write element 5. As shown in FIG. 1B, the magnetic resistance element 2 is composed of a magnetic resistance film 3 and a pair of conductor films 4 connected to the opposite ends of the magnetic resistance film 3. The magnetic resistance element 2 is an element whose resistance changes according to an external magnetic field. Accordingly, by using the magnetic resistance element 2, an electric current having a magnitude corresponding to the magnetization of a track T on a magnetic disk, for example, can be output to thereby allow reading of data recorded on the magnetic disk.
The magnetic resistance element 2 is capable of only reading data. Therefore, the write element 5 is additionally provided to write data as required. The write element 5 is an inductive head, for example. The write element 5 has a lower magnetic pole 6 and an upper magnetic pole 8 opposed to the lower magnetic pole 6 with a gap defined therebetween. A coil 7 is provided between the lower magnetic pole 6 and the upper magnetic pole 8 to excite these magnetic poles 6 and 8. The coil 7 is surrounded by a nonmagnetic insulating layer 9.
In such a composite magnetic head, it is desirable to make constant the resistance of the magnetic resistance film 3 of the magnetic resistance element 2. However, it is difficult to make the resistance constant only in a manufacturing process for the thin film of the magnetic head. Accordingly, after forming the thin film of the magnetic head, it is machined so that the height (width) h of the magnetic resistance film 3 becomes constant, thus obtaining a constant resistance.
FIGS. 2A to 2C and 3A to 3D illustrate a manufacturing process for the composite magnetic head shown in FIGS. 1A and 1B.
As shown in FIG. 2A, a set of many row bars 11 each having a plurality of composite magnetic heads 12 (see FIG. 2B) are formed on a wafer 10 by a thin-film technique. In the next step, the wafer 10 is cut into many rectangular parts to thereby separate the above set into the row bars 11 as workpieces. As shown in FIG. 2B, each row bar 11 has a plurality of magnetic heads 12 and three resistance elements 12a for monitoring of lapping. These magnetic heads 12 and resistance elements 12a are arranged in a line. For example, the resistance elements 12a are positioned at the left end, center, and right end of the row bar 11.
Each row bar 11 having the plural magnetic heads 12 is next subjected to lapping so that the height of the magnetic resistance film 3 in each head becomes constant as mentioned above. However, since the row bar 11 is as thin as 0.3 mm, for example, it is difficult to mount the row bar 11 directly on a lapping machine. Accordingly, as shown in FIG. 2C, the row bar 11 is temporarily bonded to a row tool 13 as a lapping jig by means of a hot-melt wax.
In the next step, the row bar 11 bonded to the row tool 13 is lapped on a lap plate (or polish plate) 14 as shown in FIG. 3A. In this lapping operation, the resistance of each resistance element 12a of the row bar 11 is measured at all times as known from Japanese Patent Laid-open No. 2-124262 (U.S. Pat. No. 5,023,991) and Japanese Patent Laid-open No. 5-123960, for example. Then, whether or not the height of the magnetic resistance film of each magnetic head 12 has become a target value is detected according to the measured resistance of each resistance element 12a. 
At the time it is detected that the magnetic resistance film has been lapped up to the target height, according to the measured resistance, the lapping operation is stopped. Thereafter, as shown in FIG. 3B, a slider is formed on a lower surface 11-1 of the row bar 11.
In the next step, the row bar 11 is cut into the plural magnetic heads 12 in the condition that it is bonded to the row tool 13 as shown in FIG. 3C. In the next step, the row tool 13 is heated to melt the hot-melt wax, thereby removing the magnetic heads 12 from the row tool 13 to obtain the individual magnetic heads 12.
In this manner, the row bar 11 having the plural magnetic heads 12 arranged in a line is first prepared, and next subjected to lapping, so that the magnetic resistance films 3 of the plural magnetic heads 12 can be lapped at a time.
However, there are variations in height among the magnetic resistance films 3 of the plural magnetic heads 12 in the row bar 11 on the order of submicrons, depending on a mounting accuracy, film forming accuracy, etc. It is accordingly necessary to correct for such variations in the lapping operation for mass production of magnetic heads uniform in characteristics.
In this respect, it is known that a hole is formed through the row tool 13 at a position near a work surface to which the row bar 11 is bonded, and that a force is applied from an actuator through this hole to the row tool 13, thereby producing a desired pressure distribution between the row bar 11 and a lapping surface of the lap plate 14. However, since the hole of the row tool 13 is singular, the variations cannot be reduced and it is difficult to obtain a high working accuracy.
To cope with this problem, it has been proposed to form a plurality of holes through the row tool 13 and respectively apply forces from actuators through these holes to the row tool 13 as described in U.S. Pat. No. 5,607,340. However, these actuators are required to have capacities of applying relatively large forces to these holes, in order to obtain a desired pressure distribution, and it is therefore difficult to manufacture such actuators acting on a plurality of load points (or operation points). As a result, the spacing between any adjacent ones of the plural load points (the plural holes) cannot be greatly reduced, yet causing a difficulty of improvement in working accuracy.
Further, in polishing magnetic heads, a working accuracy on the order of submicrons is required from the viewpoint of the property of the workpiece. The following items may be considered to maintain a high accuracy always stably, provided that mass production is carried out.
(1) Working control hardly depending on shape characteristics of the workpiece and external factors.
(2) Working control with a reduced load on the workpiece itself.
(3) Working control less susceptible to an unexpected accident such as abnormality of monitor elements.